Polyaryl ether ketones (PAEK), such as PEEK, which is the most commercialized, are well known polymers such as described in Chapter 37 of the “Handbook of Thermoplastics” published by Marcel Dekker Inc. These polymers are highly aromatic mostly semi crystalline thermoplastics which, because of their aromatic polymer backbone, have transition temperatures as high as 240° C. These polymers may be synthesized by well known condensation polymerization methods. PAEK has excellent resistance to acids, water and is capable of being sterilized by gamma radiation, ethylene oxide gas and steam.
Reinforced polyetheretherketone (PEEK) has been proposed for us in orthopedic implants such as hip stems and acetabular cups. U.S. Pat. Nos. 5,181,930 and 5,443,513 relate to hip stems made of PEEK including carbon fiber reinforcements. PEEK has also been proposed for use in acetabular cups as either backing or bearing materials. See for example, U.S. Pat. Nos. 6,638,311 and 6,758,864. Flexible acetabular cups made of PEEK have also been proposed as discussed in U.S. Publications 2007/073410 and 2007/0191962. In these proposals the opposite bearing, such as a femoral head, have been made of either a ceramic or metal bearing surface.
U.S. Patent Publication 2009/0164023 relates to an all polymeric bearing couple wherein each part is made of a composite material including carbon fiber reinforcement.
PEEK and carbon fiber reinforced PEEK composite as a potential bearing surface for total joint replacement applications was considered in the 1990s (Wang, A., Lin, R., Stark, C., and Dumbleton J H., Wear 225-229 (1999) 724-727). The intention was to replace the ultrahigh molecular weight polyethylene bearing (UHMWPE) with PEEK or carbon fiber reinforced PEEK composite bearings in traditional metal or ceramic-on-UHMWPE bearing couples for total hip and total knee joint replacements. It was found that pure PEEK without carbon fiber reinforcement against a ceramic counterface produced higher wear rate than a traditional ceramic-on-UHMWPE bearing couple while a ceramic-on-carbon fiber reinforced PEEK composite yielded a lower wear rate than a traditional ceramic-on-UHMWPE bearing couple. Metallic bearing counterfaces such as CoCr or stainless steel was found unsuitable against carbon fiber reinforced PEEK composite bearing due to significant scratching of the metallic surface by the harder carbon fibers. Carbon fiber reinforced PEEK-on-PEEK has only been considered for either smaller non-weight bearing or low weight-bearing joints (Qi-Bin Bao, et al, Nubac Disc Arthroplasty: Preclinical studies and preliminary safety and efficacy evaluations, SAS Journal, Winter 2007, Volume 01, issue 01, p. 36-45). A low-to-high wear transition was found for PEEK-on-PEEK as the applied load increased in a wear test study (Heather Austin, et al, Exploring the wear of a peek all-polymer articulation for spinal application, Society for Biomaterials 2009 annual meeting, Apr. 22-25, 2009, San Antonio, Tex.).
PTFE-on-PTFE was first used for total hip replacement by Dr. John Charnley prior to 1962 (Steven M. Kurtz, The UHMWPE Handbook, p. 53-70). Because of poor wear performance; PTFE-on-PTFE has been abandoned. US patent publications 2007/0270970 and 971 relate to polymeric spine bearing components.
Polyacetal-on-Polyethylene was introduced as an all polymer bearing couple in total knee arthroplasty in the 1980's and clinical results were published in the 1990's (1) H. McKellop, et al, Super wear properties of an all-polymer hip prosthesis, 31st Annual ORS, Las Vegas, Nev., Jun. 21-24, 1985, page 322; (2) D. J. Moore, et al. The total knee replacement prosthesis may be made entirely of polymer. The Journal of Arthroplasty, Vol. 13, No. 4, 1998). Because poor gamma sterilization resistance of the polyacetal material (Delrin) and inadequate fixation of the Delrin femoral component to the bone, the use of Polyacetal-on-Polyethylene has been discontinued.